Strategy for D-shape assembly of ITER vacuum vessel sector #06 as applying 3D metrology

Highlights: • Method for d-shape assembly of ITER vacuum vessel is introduced. • The virtual fit-up method is explained. • Applying results of 3D metrology are introduced. The first sector of the ITER vacuum vessel (VV) has been delivered to the ITER Organization. One of the critical manufacturing steps is d-shape assembly. The manufactured four poloidal segments (PS 1, 2, 3, 4) are assembled, and then form the d-shape structure with a height of 11.4 m. Each PS is a complex and heavy double-wall structure with an inner shell and outer shell, poloidal and toroidal ribs, and in-wall shielding blocks are filled inside of the double wall as radiation shield. Thus, it is quite difficult to handle for assembly in keeping with the segment final dimensional status, so that it is necessary to set a practical plan. Before conducting actual assembly, the d-shape is virtually fitted using all results of final 3D metrology on each PS. In detail, each inner shell as-built result on four interfaces, plus a margin for welding shrinkage and gap for welding are considered to set the d-shape fit-up reference. To set each PS in the right position as comparing the fit-up reference, the fiducial posts (FPs) on each PS are measured using a 3D metrology system. After done the fit-up on the assembly plate, whole FPs (55 ea.) are checked as verification. As a result, the PS2 and PS4 are shifted Avg 7.4 mm and Avg 7 mm to the poloidal way, respectively. After finished inner shell welding, the whole FPs are also measured. The PS2 and PS4 are still shifted Avg 1.4 mm and Avg 0.8 mm to poloidal way, respectively. Eventually, the as-built dimension on the important part is evaluated with given tolerance as a preliminary prediction of the final d-shape result.